The conventional Leclanche cells which are widely employed as primary dry cells for flashlights and other uses make use of a metallic zinc anode which is normally the can used as a container for the cell, and a manganese dioxide cathode together with an electrolyte which is essentially ammonium chloride together with some zinc chloride, often in a gelled or paste condition. Electrically conductive carbon such as graphite is added to the manganese dioxide to increase the conductivity thereof and a carbon rod is often used as the current collector for the cathode. Alkaline Leclanche cells are also known, the electrolyte here being potassium hydroxide. A disadvantage of these systems is that a rather small fraction of the theoretically available oxidation capacity of the manganese dioxide is actually used. The end-product of discharge approximates in composition, or approximates at least in oxidation state, to Mn.sub.2 O.sub.3 ; that is the valence state of the manganese is reduced from a nominal value of 4 (if the manganese dioxide is stoichiometric MnO.sub.2) to about 3. Actually the manganese dioxide always contains less than the stoichiometric amount required by the formula MnO.sub.2 and therefore the valence change in practice is less than unity. To overcome some of the disadvantages of the conventional and alkaline Leclanche cells, and acid Leclanche system has also been proposed wherein the electrolyte is sulphuric acid and the zinc anode is amalgamated to reduce corrosion which takes place even when the cell is not under load. The acid Leclanche cell has an open circuit potential or E.M.F. of nearly 2.2 volts and the working voltage on moderate range starts at 2.0 to 2.05 volts. A large fraction of the active material is used over a 10% voltage drop to 2.0 to 1.8 volts.
Where cells of these types must be made very compact, carbon rods are an undesirably bulky current collector and accordingly it would be desirable to employ current collectors of higher electrical conductivity, which in practice means metallic current collectors. However, a number of materials have been tried, including silver and platinum, but most metals suffer from severe corrosion, particularly in the acid system, and this leads to premature failure in the cells. From the performance point of view, plantinum was found to be satisfactory but is undesirably expensive.